OP_CODESEPARATOR is not used any more from what I can tell this was actually a security risk for bitcoin as per the post below.
The official info behind this would be as follows :
OP_CODESEPARATOR
OPCode = 171
Hex = 0xab
Input = Nothing
Output = Nothing
Description = All of the signature checking words will only match signatures to the data after the most recently-executed OP_CODESEPARATOR.
The post below will give some more info related to this OP code though it is no longer used as far as I can tell.
https://bitcointalk.org/index.php?topic=255145.msg2760786#msg2760786** Edit **
You can also read here some more info about it.
https://github.com/bitcoin/bips/blob/master/bip-0017.mediawiki